The present invention relates generally to supersonic combustion ramjet engines i.e., scramjets, and, more particularly, to a scramjet engine having an improved combustion cycle.
Ramjet and scramjet engines are known for powering aircraft at high supersonic or hypersonic velocities greater than about Mach 3. Both engines have no components therein which rotate due to airflow thereover such as in conventional turbofan and turbojet gas turbine engines. Instead, ramjet and scramjet engines utilize the supersonic movement of the aircraft in the atmosphere for compressing inlet airflow in the engine wherein it is mixed with fuel, and ignited for generating combustion gases for propelling the aircraft.
Ramjet engines and scramjet engines are fundamentally different in structure and function since a ramjet engine is conventionally designed to operate with subsonic fluid flow therethrough, whereas a scramjet engine is conventionally designed to operate with supersonic fluid flow therethrough. Ramjet engines are typically effective for powering aircraft at supersonic speeds up to about Mach 6 whereas scramjet engines are designed for powering aircraft at flight velocities from about Mach 5 up to about Mach 18 and higher.
Since the scramjet engine channels supersonic fluid flows therethrough and is designed to power aircraft at hypersonic velocities, the scramjet engine must be effective for combusting a fuel/air mixture at relatively high rates. Furthermore, conventional scramjet engines utilize oblique shockwaves from the aircraft to compress in part freestream, or ambient airflow for use in the engine. Such compression is conventionally known as recompression. Recompression of ambient airflow is effective for providing to the scramjet engine supersonic compressed airflow at a pressure of about 12 pounds per square inch absolute (psia) and at static temperatures of about 3000.degree. Rankine (R) after the inlet air has been mixed with a fuel such as hydrogen, for example, for use in the combustor of the scramjet engine.
The static temperature of about 3000.degree. R. is more than adequate for creating spontaneous ignition of the fuel/air mixture in the scramjet engine for initiating and allowing recombination reactions (i.e., combustion) of the fuel/air mixture to occur for generating heat and thrust from the scramjet engine.
The fuel/air mixture is further heated by the recombination heat release and reaches static temperatures of about 5200.degree. R. which is an equilibrium kinetic limit. Above this temperature, the rate of chemical dissociation of the combustion gases would exceed the rate of chemical recombination. Accordingly, combustion is limited by dissociation occurring at a maximum temperature of the combustion process.
Accordingly, chemical heat release, and therefore propulsive energy, are fundamentally limited by the static temperature rise available between the combustor inlet temperature and the equilibrium temperature, thusly providing a limit to the efficiency of operation of the scramjet engine.
It is not believed that a scramjet-powered aircraft has yet been built or flown. However, small research-type scramjet engines have been built and laboratory tested at simulated flight speeds up to about Mach 7. Accordingly, the references herein to conventional and typical scramjets and structures refers to information conventionally known to those skilled in the art of engines for powering aircraft at supersonic velocities, which is based, in part, on mathematical modeling and analysis.